JPS60152111A - Receiver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Technical field 1 The present invention relates to a receiver having an automatic gain control function.

[Background technology]

FM receivers and AM receivers are provided with an automatic gain control circuit (AGO) to ensure good reception in response to changes in field strength and the presence or absence of interfering radio waves. Broadly speaking, there are two types of AGO operations: wideband AGO and narrowband AUO. Wideband AGC is performed to prevent cross modulation in the mixing circuit (MIXER) and also to prevent saturation of the high frequency amplifier circuit. In other words, the desired signal f as shown in FIG. When the following signal, that is, the interference signal f1 becomes high level. Since the transistors constituting the high frequency amplifier circuit and the mixing circuit become saturated, in order to prevent this, for example, the gain of the high frequency amplifier circuit is reduced. Note that the reception of the interference signal f1 is as follows, since the frequency characteristic of the high frequency amplifier circuit is a wide band characteristic as shown by fR in Fig. 1.
The operation for maintaining excellent reception conditions despite this interference radio waves is called wideband AGO.

On the other hand, the narrowband AGO receives the desired signal f. The purpose is to maintain the output voltage of the intermediate frequency amplifier circuit at a constant level when the '1 electric field strength becomes larger than a predetermined value.

The above-mentioned wideband and narrowband AGO'& capable receiver is already disclosed as US Pat. No. 3,947,771, and FIG. 2 shows its circuit configuration.

1 is a receiving antenna, 2 is a high frequency amplification circuit, and the received signal f is supplied to a mixing circuit 3. Reference numeral 4 denotes a local oscillation circuit which supplies the . detection) total of 5t
(The ratio of 11 times with Kinan tfJI+vRzv is performed, and the output signal VC is obtained when ``a'' ItKF.

On the other hand, the output signal V2 is supplied to the intermediate frequency circuit 6, and outputs the intermediate frequency signal 1f. After the intermediate frequency signal 1f is at a high level, the output signal VAGc of the h<:>c circuit 7 is also brought to a level of 1. At this time, the gate 8 is opened by the output signal VK, and the output signal 1f (1f) is supplied to the R1 circuit 2 to perform the AGO operation.

The AGO operation in this case means that wideband and narrowband AGo are performed.

When -<vREF, when the output signal VAGO of the AGO circuit 7 becomes equal to or higher than the predetermined threshold value of the gate 8,
Output signal vAGC or gate 8? A valve is supplied to the ILF circuit 2. In this case, only narrow band 130 will be performed.

By the way, the inventor of the present invention has conducted thorough technical studies regarding the above-mentioned AGO operation. the result.

It was revealed that it had the following defects.

That is, the desired signal f. If the level of the interference signal f is so low that the gate 8 cannot be opened, and the interference signal f is at an island level, the AGO operation is not performed on the R1 circuit 2. As a result, the inventor's studies have revealed that a so-called mixed 8 state occurs, and the audio output of the interfering signal appears superimposed on the desired signal.

[Purpose of the invention]

An object of the present invention is to perform wideband AGO and narrowband AGO separately even when a desired received signal is at a low level and an undesired interfering signal is at a high level, thereby achieving good reception without interference. The aim is to provide the opportunity.

The above and other objects and novel features of the present invention will become apparent from the present specification and the accompanying drawings.

[Summary of the Invention] A brief summary of the invention disclosed in this specification is as follows.

That is, the desired ID signal and the interference signal contained in the received signal are detected by individual comparisons with the reference voltages vref 11 and Vref 2, and when the desired signal is at a low level and the interference signal is at a high level, the interference signal is detected based on this interference signal. The detected output performs AGO operation on the high frequency amplifier circuit to prevent interference when the desired signal is at a low level.

This achieves the object of the present invention.

[Embodiment 1] Hereinafter, a first embodiment of a receiver to which the present invention is applied will be described with reference to FIG. Note that the receiver in this embodiment is an FM receiver.

11 is a receiving antenna, and a received signal f is supplied to a high frequency amplification circuit (hereinafter referred to as a TtF circuit) 12. Now, let us consider a case where the received signal f is combined with a desired signal and an interfering signal.

Output signal f of RF circuit engineer 2. is supplied to the mixing circuit 13, and the local signal obtained from the local oscillation circuit 14 is also supplied to the mixing circuit 13.

An intermediate frequency signal lf is obtained from the mixing circuit 13.

This lf is supplied to a bandpass filter 15 having a narrow frequency bandwidth. Further, the intermediate frequency signal l
f/ is fed to a second AGO detector 16, which lf
The temperature control signal ■1f' is output according to the level of /. Moreover, the band pass filter 15 is.

It is provided to pass only the desired signal.

Here, intermediate frequency signal 1. / and bandpass filter 15
Comparing the output signal 1fB of 1, the former has the frequency components of the desired signal and the interference signal, while the latter has only the frequency components of the desired signal.

The difference is that the interfering signal is removed.

The output signal 1fB is amplified (1fB) by the intermediate frequency circuit 17.
(B') and is supplied to the subsequent FM detector (not shown), and its voltage level is applied to the first AGO detector 1.
8. And from the AGO detector VXf
B' is output. Note that the offset voltage v1o between the first voltage comparator 210 reference turtle pressure ■ref and v1fB'
ffset and the second voltage ratio 1t',! Offset voltage ■zof between the reference voltage Vref+ and vIf' of the second device 22
The relationship between fset and fset is -12offset and 1offset.

Next, the AGO operation will be described.

As already mentioned, it is assumed that the received signal f contains a desired signal and an interfering signal. Now, suppose that the desired signal and the interfering signal are at a low level, and the difference is -1°.
Vref2, the first and second voltage comparators 21°2
No detection output is obtained from 2. Then, the AGO operation is not performed on the RF circuit 12, and the RF circuit 12 operates with high gain.

Next, the circuit operation when the desired signal contained in the received signal f is at a low level and the interfering signal is at a high level will be described.

In this case, the output of the second AGO detector 16 is v, .
' and the reference voltage ref2 become vXf'nVref2, and the output v width of the first AGO detector and the reference voltage vre
fs is Vrefl>■1fB'. Therefore, a detection output vA is obtained from the second voltage comparator 22 on line B,
The detection output V cannot be obtained from the first voltage comparator 21. The detection output (1) is supplied to the AGO amplifier 20 via the OR circuit 19. Then, the AGO signal A (1c) is obtained, and its voltage level lowers the gain of the RF circuit 12. In other words, a wideband operation is performed using the interference signal.

Next, we will describe the circuit operation when the desired signal is at a high level exceeding a predetermined value and the interference signal is at a low level.

In this case, the output ■1f' of the second AGO detector 16 and the reference voltage vref2 are ■refz >■rf', and the output ■xfB' of the first AGO detector 21 and the reference voltage ■ref 1 are ■ 1fB'〉■ref1. Therefore, the second voltage comparator 22 does not obtain the detection output (2), and the first voltage comparator 21 obtains the detection output VB.

As a result, the AGO signal ■AG is generated from the GO amplifier 20.

is obtained, and the gain of the RF circuit 12 is lowered by the voltage level. That is, the AGo operation is performed based on the desired signal.

Next, the circuit operation when both the desired signal and the interfering signal are at a higher level than a predetermined value will be described.

In this case, 1st + 7) AGO detector 1B (1) output vs.
fB'+output V1 of the second AGO detector 16. / and the reference voltage vref2・Vrefl・■tfn′〉vre
fl, "xl'> vrefl.

Therefore, the detection output V from the first voltage comparator 21 to line A.
B is obtained, and the second voltage comparator 22 also obtains a detection output vA on line B. The detection outputs vA and VB are simultaneously supplied to the AGO amplifier 20 via the OR circuit 19'.

Then, the AGO signal VAGC is obtained from the AGO amplifier 20 and reduces the gain of the RF circuit 12. That is, an AGO operation is performed using the desired signal and the interference signal.

As the AGO operation as described above is performed, the level of the interference signal becomes high and the internal transistors of the RF circuit 12 and the mixing circuit 13 are about to be saturated, and the detected output vA is compared with the reference voltage Vrefz. As a result, the gain of the RF circuit 12 as described above is reduced. Therefore, in the receiver to which the present invention is applied, the RF circuit 12.
The internal transistor of the mixing circuit 13 is not saturated,
Generation of waveform distortion and noise components can be prevented.

Further, since the detection output (2) does not change the output of the intermediate frequency circuit 17, there are other advantages such as the fluctuation of the final desired output signal (corresponding to the output signal IfB' in this embodiment) due to the interference signal is small. be.

[Embodiment 2] Next, a second embodiment of the present invention will be described with reference to FIG. 4. Note that this embodiment applies the present invention to an AM receiver, and since the circuit configuration shown within the imaginary line in FIG. 4 is well known to those skilled in the art, a description thereof will be omitted.

It is assumed that the AGO detector 27 is supplied with a frequency signal fo' containing a desired signal and an interference signal from the RF circuit 30. Further, a detection output (audio signal) Vd is obtained from the AM detector 26 and is supplied to a subsequent audio amplifier (not shown), and at the same time, it is passed through an OR circuit 29 to an AGO signal.
The signal is supplied to an amplifier 28. The AGO signal VAGC is supplied to the RF circuit 22 and the intermediate frequency circuit 25. First, the intermediate frequency circuit 25 performs the AGO operation, and from this state the AG
When the 0 signal VAGC becomes higher level, the RE' circuit 30 performs the AGO operation.

In the AM receiver of this embodiment, the AGO operation based on the desired signal, that is, the AGO operation based on the detected output vd, is performed by comparing the threshold-hold voltage in the RF circuit 30 and the intermediate frequency circuit 25 with the detected output vd. Therefore, the reference voltage vref1 described in the first embodiment is not provided.

Further, the reference voltage vref2 is set at a higher level than the threshold voltage. As a result, if both the desired signal and the interfering signal are at low levels, no AGO operation is performed. Further, when the desired signal is at a low level and the interference signal is at a high level, a detection output vA is obtained from the AGO detector 27, and IFAGO operation and RFAGO operation are performed depending on the voltage level.

When the desired signal is at a high level and the interfering signal is at a low level, the detection output V causes IFAGO operation or IF
Both AGO and RFAGO operations are performed.

When both the desired signal and the interference signal are at high level, the IFAGO operation and the RFAGO operation are performed simultaneously by both the detection output vd and the detection signal (2).

〔effect〕

(1) The level of the desired signal and interference signal contained in the received signal is detected, and the wideband AGO and narrowband AGO are performed individually or simultaneously. The AGO operation can be performed even when the RF circuit is in use, and the effect of preventing saturation of the internal transistors constituting the RF circuit can be obtained. It is also possible to prevent interference.

Although the invention made by the present inventor has been specifically explained above based on the embodiments thereof, the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways without departing from the gist thereof. Needless to say.

For example, in the first embodiment, the intermediate frequency signal 1f
/, the IFAGO operation may be performed in the intermediate frequency circuit.

Furthermore, the signal for performing wideband AGO is not limited to the intermediate frequency signal lf', but may also be an output signal of an RF circuit or an RF
Internal signals of the circuit or mixed circuit may also be used.

[Application field]

In the above explanation, the invention made by the present inventor will be mainly described in the field of application which is the background of the invention, such as FM receivers and AM receivers.
Although the case where it is applied to a receiver has been described, it is not limited thereto.

For example, it can also be used for television receivers.

It can also be used for car radios, various communication devices, etc.

[Brief explanation of drawings]

FIG. 1 is a frequency characteristic diagram illustrating the relationship between a desired signal and an interfering signal in a received signal, and FIG.
FIG. 3 is a block diagram of an FM receiver showing a first embodiment of the receiver to which the present invention is applied, and FIG. 4 is a block diagram of a second embodiment of the present invention. 1 is a block diagram of an AM receiver. 11.31...Receiving antenna, 12.30...High frequency amplification circuit, 13.23...Mixing path, 14,24...
...Local oscillation circuit, 15...Band pass filter, 1
6, 18.27...AGO detector, 20.28...
AGO enhancer, 19.29...OR circuit, 21°22
...Voltage comparator, VA, V, ...AGO detection output,
V-AGO signal, ■ref1. V, ef2...Reference voltage. Mu GC

Claims (1)

[Claims] 1. Detect the presence or absence and level of the desired signal and interference signal included in the received signal, and when the desired signal is low level and the interference signal is at h level, the gain of the high frequency amplification stage is determined based on the detection signal of this interference (m). A receiver configured to automatically control.